1. Field of the Invention
The present invention relates, in general, to a radio apparatus and, in particular, to a circuit mounting structure of the same. More specifically, the present invention relates to a printed circuit board (PC board) and a circuit assembly for a radio apparatus, which PC board and assembly are particularly advantageous for use in mobile radio communication units, such as citizen band transceivers, mobile telephones, or portable telephones.
2. Description of the Related Art
The above-mentioned types of radio communication units are required to have a compact structure and high performance characteristics. In particular, for a portable telephone, a receiver, a transmitter, a controller, and a power source must be assembled into a single unit having a handy or pocket size structure. Accordingly, the mounting of the electrical components or circuits thereof in a high density is an important problem.
Further, in a radio apparatus, the electromagnetic shield of a radio frequency (RF) circuit is also a very important problem. This problem becomes greater as the mounting density of the electrical components or circuits becomes higher and the radio frequencies increase.
According to a conventional mounting structure, an RF circuit consists of a plurality of modules having predetermined functions. A conventional RF circuit module has a modular circuit assembly including a PC board of dielectric material having conductor patterns, and electrical components and terminal pins are mounted thereon in electrical connection with the conductor patterns. This modular circuit assembly is mounted in a metal shielded package for electromagnetic shielding, with the terminal pins projecting out of the shielded package.
The RF circuit modules are mounted on a mother PC board of dielectric material having conductor patterns. In a conventional mounting structure, the terminal pins of the RF circuit modules are inserted into plated throughholes in the mother PC board, in such a manner that the ends of the terminal pins project beyond the back surface of the mother PC board, i.e., the surface opposite to the circuit module mounting surface, and are soldered to the conductor patterns on the back surface of the mother PC board. In many cases, the mother PC board has a ground layer on the circuit module mounting surface thereof, to which the circuit modules are electrically grounded.
In another conventional mounting structure, the mother PC board is provided with terminal jacks, into which the terminal pins of the RF circuit modules are connected, to facilitate the connection and disconnection of the RF modules. In this case, also, the terminal jacks are mounted on the mother PC board, and the ends thereof project beyond the back surface of the mother PC board and are soldered to the conductor on the back surface of the mother PC board.
That is, in the above-mentioned mounting structures, the terminal pins or jacks have projections exposed on the backside of the mother PC board. This structure has a problem in that the exposed projections of the terminal pins or jacks cause undesirable electromagnetic interference between the RF circuit modules to be produced. Further, the projections of the terminal pins or jacks cause dead spaces to be produced, from the viewpoint of the mounting structure, thereby obstructing the achievement of a high density mounting. Furthermore, there is a disadvantage in that handling of the RF circuit module with the terminal pins projecting therefrom is inconvenient during the manufacturing and mounting steps. For example, the terminal pins are apt to be damaged at this point.